Endoscopes, boroscopes, laparoscopes, and related visualization devices are used to visualize locations that may not be directly visible to the human eye. One method to relay an image uses coherent fiber bundles. These are flexible and can be long enough to allow the image chip to be part of an external base unit. Unfortunately, coherent fiber bundles frequently suffer from a coarse, often random pixel structure, and hence are viewed as a compromise between image quality and a small diameter flexible form. Another image relay approach is to use discrete lens elements in a short rigid cylindrical form. Over short relays, quite good image quality can be relayed. However, longer relays or smaller diameter leads to compromises. These problems have led to the appearance of video imagers.
Video medical imaging systems such as video endoscopes and video laparoscopes have been in general use since the 1980s. Laparoscopes are rigid devices that may be used in minimally invasive surgery. Typically, laparoscopes use a proximal, externally mounted hand piece that includes a digital camera. The digital camera collects video images through a series of rod lenses arrayed end-to-end inside a tube that extends into a body cavity of the patient. The camera returns its signal through wires to a console that often includes a display monitor. Also typically mounted on the console is a light source, often based on a xenon lamp. The light source sends light to the hand piece through an optical fiber, where a coupling is made. The light is then sent into the body cavity through optical fibers that run inside the laparoscope tube. Often, the optical fibers terminate at the distal end of the tube in a concentric ring, or partial arc around the periphery of the tube. In use, the illumination power is adjusted to give an image of appropriate brightness on the video monitor.
Endoscopes are typically flexible devices that may be used in diagnostic or other procedures. Modern endoscopes (and some laparoscopes) use a distal tip digital camera that collects light, converts it to an electronic signal, and sends the electronic signal up the flexible tube to a hand piece. The signal is then sent to a console for display similar to the manner of operation of laparoscopes. Illumination is sent to the body cavity in a manner similar to that of laparoscopes, except the illumination fibers typically terminate as a pair of apertures on each side of the camera lens. Endoscopes often include irrigation channels and working channels for instruments, in addition to a steering apparatus that may be used to aim the tip of the endoscope in the direction the clinician wishes to look or push the tube.
Endoscopes and laparoscopes may be end-looking or side-looking. In end-looking devices, the field-of-view is positioned directly in front of the end of the device. Side-looking devices may have their fields-of-view located 70°, or other angle off-axis from the end of the tube. The field-of-view varies according to the application. For instance, colonoscopes (a type of endoscope used to examine the colon) often have a 140° diagonal field-of-view, while laparoscopes may have fields-of-view closer to 70° diagonal.
Instruments may be passed down the working channel of many endoscopes. Forceps and other devices have been developed that may pass within the diameter of the working channel into the body cavity where the clinician uses them to take tissue samples, etc. In the field of laparoscopy, instruments are generally introduced to the procedure through separate small incisions. Often the instruments as well as the laparoscope pass through trocars, or rings that line the incisions to prevent undue binding or damage as well as maintain a seal.
Laparoscopes and endoscopes may use a pixelated sensor array such as a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) device. In pixelated imagers, each pixel corresponds to an element of an array and each element receives light energy from a conjugate point in the field-of-view for a selected sampling interval. Each element converts light to an electrical signal proportional to the brightness of its conjugate point. This approach may force compromises in meeting the size and image quality requirements. In many cases, achieving the highest performance with such technologies implies imaging chips that are large. Some large chips depend on an optical system to relay the image from the interior of the body to the camera chip. In many cases, such sysetems also depend on strong illumination, typically derived from a 300-watt arc lamp coupled in by fiber bundle.
One announced video endoscope product has a pixel count of 850,000 and fits in a probe with tip diameter of 5.9 mm. To increase the number of pixels or decrease the probe diameter, one approach is to reduce the pixel size on the imaging chip. Smaller pixels (below 4 microns) frequently run into difficulties with electron diffusion, and hence scaling down may compromise resolution, such as by limiting sampled point density, for example, contrast ratio, and/or other aspects of the image. Pixel array technology may also suffer from the limitation of fixed pattern noise. This may have the form of both offset fixed pattern (which may dominate in low level regions) and gain fixed pattern (which may affect even high signal areas of the scene). Typical non-uniformity may approximate or exceed 1% of the average signal level. Thus with CCD and CMOS technologies it is frequently considered challenging to increasing the sampling density while also reducing instrument size.
Color distal video chip systems present further challenges. One choice is to use a single chip sensor and divide the sample points spatially by a factor of 3 (or by 4 in red and blue channels and by 2 in the green channel), with red, green, and blue color filters over individual pixels. This typically causes a loss of ⅔ of the light at the sensor plane. Conversely, a three-chip sensor, such as is used in high-quality cameras, is frequently bulky compared to a single chip and is incompatible with size constraints. Time sequential color is another approach, but this allows only ⅓ of the time for photon collection, or alternatively ⅓ the video rate. Another challenge is in crating a driver for a high bit rate data link that must somehow be contained in the small volume of the distal tip.
Thus, today's digital endoscopes and laparoscopes may suffer from limited image quality and dynamic range and often exhibit other undesirable artifacts. In the case of distal imaging systems in particular, diameter limitations have been a common hindrance to higher resolution. Conversely, resolution requirements have hindered diameter reductions.
Overview
According to one aspect, a scanned beam imaging device, which may be fabricated in the form of an endoscope for example, has advantages over present CCD imaging technology. Advantages can include some or all of an increase in image resolution, an increase in image quality, a reduction of light source power, and a reduction in package diameter.
According to another aspect, a scanned beam endoscope has a diameter of 5 millimeters.
According to another aspect, a scanned beam endoscope has a scanner capsule with a diameter of 2.5 millimeters (mm).
According to another aspect, a scanned beam imaging system may include a photonics module with red, green, and blue laser light sources at 635 nanometers (nm), 532 nm, and 473 nm wavelength, respectively.
According to another aspect the photonics module may combine light from the laser light sources using dichroic mirrors and launch the combined light into a single mode optical fiber.
According to another aspect, the combined light is transported down the single mode optical fiber to a distal location, which may be in a non-readily accessible location such as inside a body.
According to another aspect, light emerging from the distal end of the single mode optical fiber is formed into a beam and reflected off a first reflecting surface onto a bi-axial MEMS scanner. The bi-axial MEMS scanner then scans the beam over a two-dimensional field of view.
In one particular embodiment, the MEMS scanner had a 1.56 mm square mirror and scanned the beam at a horizontal (fast) scan angle of 6 degrees zero to peak mechanical at a (fast scan) frequency of 19.7 kilohertz (kHz). The vertical scan approximated a sawtooth waveform and progressively scanned the beam at a slow scan frame rate of 60 hertz (Hz).
According to other embodiments, the horizontal and vertical scans may be run at frequencies of several times the frame rate to produce a Lissajous scan pattern from which an image may be decoded.
According to one embodiment, the light from the distal end of the fiber passes through a hole in the MEMS scanner. The first reflecting surface is the inside of a meniscus lens that reflects a portion of the light, the rest of the light propagating through to the field-of-view as a non-scanned pattern. The reflected portion of the light is reflected to the MEMS scanner and scanned across at least a portion of the meniscus lens as a diverging beam. Scanned light that passes through the meniscus lens is focused to form a scanned beam with a desired shape, for example a semi-collimated beam having a waist of desired size at a desired distance. The shaped scanned beam thus sequentially illuminates spots on the target object.
According to one embodiment, the scanned beam had a power of 1 to 3 milliwatts (mw) that impinged the test object at a distance of 10 to 100 mm.
According to one embodiment, scattered light from the scanned beam was collected by several 3 mm diameter multimode fibers. The collected light propagated along the multimode fibers a distance of approximately 1 meter where it was converted to electrical signals by detectors.
According to one embodiment, the detected light was digitized and reconstructed to form an image of the test object with a resolution of 800 by 600 output pixels.
According to another embodiment, a scanned beam imaging device includes separable controller and tip sections.
According to another embodiment a controller can support a variety of tips.